Background: Ovarian cancer is the most lethal gynecological cancer, causing over 200,000 deaths worldwide in 2020. Initial standard treatment for primary ovarian cancer is optimal cytoreductive surgery (CRS) preceded and/or followed by intravenous platinum-based chemotherapy. However, most women develop recurrence within the peritoneal cavity and die of disease. Results of the OVIHIPEC 1 trial (2018) showed improved survival of 34% when hyperthermic intraperitoneal chemotherapy (HIPEC) was given immediately following interval-CRS in women with stage III disease. However, it is unknown if the effect of HIPEC is due to hyperthermia, one extra cycle of intraperitoneal (IP) chemotherapy, or other factors. There is also concern that hyperthermia might be associated with an increase in adverse events (AEs) due to a heightened systemic inflammatory response. HyNOVA is a seamless, multi-stage randomized study that attempts to answer these questions by comparing HIPEC to normothermic intraperitoneal chemotherapy (NIPEC), focusing on safety (stage 1), then assessing activity (stage 2) and effectiveness (stage 3). In this initial study, we hypothesize that NIPEC will result in a lower rate of severe AEs compared to HIPEC. Methods This initial stage of HyNOVA is a phase II study of 80 women with International Federation of Gynaecology and Obstetrics stage III epithelial ovarian cancer, with at least stable disease following 3–4 cycles of neoadjuvant chemotherapy, achieving interval-CRS to <2.5 mm residual disease. Participants are randomized 1:1 to receive IP cisplatin 100 mg/m2 for 90 minutes either as HIPEC, heated to 42°C (41.5°C–42.5°C), or NIPEC, at 37°C (36.5°C–37.5°C). The primary outcome is the proportion of AEs ≥ grade 3 occurring within 90 days. Secondary outcomes are AE of interest, surgical morbidity, patient reported outcomes, resource allocation, feasibility, progression-free survival and overall survival. AEs are measured using both CTCAE v5.0 and Clavien-Dindo classification, particularly infection, pain, bowel dysfunction, and anemia. Tertiary outcomes are potential predictive biomarkers measured before and after HIPEC/NIPEC including circulating cell-free tumor DNA, tissue factors, and systemic inflammatory markers. There are 4 participating Australian sites with experience in CRS and HIPEC for peritoneal malignancy. HyNOVA is funded by an MRFF grant (APP1199155).